In a packaging container such as a plastic bottle made of polyethylene terephthalate, a glass bottle, or a pouch, since a space that is not filled with the contents of the container, a so-called head space, is formed in the container after sealing, and oxygen remaining in this head space oxidizes and deteriorates the contents, the long-term preservability of the above-described contents is insufficient. For this reason, a container cap as shown in Patent Document 1, Patent Document 2, and Patent Document 3, that is, an oxygen-absorbing container cap containing an oxygen absorbent in a cap of a beverage bottle container, etc., has been proposed conventionally in order to remove the oxygen remaining in this head space.
For example, a container closer containing an oxygen absorbent is described in Patent Document 1, and a container cap, in which oxygen permeability is lowered by containing an ethylene-vinyl alcohol polymer although it is not an oxygen absorbent, is described in Patent Document 2. Further, a container cap, in which an oxygen absorbent, an ethylene-vinyl alcohol polymer, and the like, are contained and a slight unevenness is formed on the surface of an oxygen-absorbent -containing resin layer is described in Patent Document 3.    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 01-315438    Patent Document 2: JP-A No. 02-225568    Patent Document 3: JP-A No. 04-327149